Machine tools currently employ cutting fluid to cool and lubricate the cutting tools. This fluid is directed in jets at the cutting tools during machining, and the cutting fluid draining from the part and tools is collected and directed to filtration equipment for removal of contaminants and chips and then returned for reuse, in the well known manner. The coolant typically includes an oil-water mix and an oil mist is often generated by the fine oil particles becoming dispersed in the air. This oil mist must be collected in order to avoid polluting the air and also to prevent deposit of oil on the adjacent surfaces which would present a safety problem particularly if oil slicks on the floor are created. In manufacturing setups, a number of machine tools are arranged as in a transfer line where workpieces are successively moved along a series of stations where respective machine tools are located, and wherein various machining processes are carried out.
Heretofore, oil mist collection has taken two different approaches. In the first approach, the air around each of the machine tools is drawn into ducting and directed to a central demister where the mist is caused to be removed from the air and the air is then filtered before being discharged back into the ambient air.
This approach has several disadvantages. Firstly, the longer the air has an oil mist present in it, the more oil passes into the air as a vapor which cannot be removed by simply filtering the air, leading to possibly unacceptable levels of air pollution and necessitating other equipment to remove the oil vapor.
Secondly, the oil collected by the demister must be disposed of, creating a maintenance burden. Fine machining particles may also collect in the ducting, also adding to the maintenance burden.
A second approach is to provide a mist collector and air filter equipment at each machine tool or station to avoid the need for directing the mist over some distance through ducting. This has the disadvantage of increased costs and complexity as electrically powered blowers are involved and wiring and controls must be provided at each machine tool.
Also, air filters must be replaced regularly, and if large numbers of filters are involved, this creates a substantial maintenance burden, which is highly undesirable in a manufacturing facility.
Another approach has been proposed in which mist collectors are provided at each station or machine to drain to the machine tool sump or coolant return with the air ducted to central air filter which would avoid some of the drawbacks of the other two approaches.
Mist collectors heretofore employed have typically been used in refrigeration and in association with internal combustion engines. In the machine tool application there is an added difficulty in that cutting chips and other particle debris from machining will often be present in or collected with the oil mist. The chips must be accommodated in any installation, and if collecting in the ductwork or tanks, they must be periodically removed. If reaching the demister, they must also be disposed of.
In any oil mist collector, the collected oil must be allowed to drain into a collection tank. A difficulty involved in this task is that air which is being drawn to the air filter must preferably not be drawn back over the collected oil in order to minimize the formation of oil vapor and/or the regeneration of an oil mist from the collected oil. If chips are simply allowed to drop into an opening to a collection tank, the air drawn from the demister to be filtered will draw in air from the collection tank through the drain opening which will impede oil and chip draining and mix the air with the collected oil.
Electrically controlled drain valves for a collection tank have been used to be open only when oil is covering the drain to prevent any air from being drawn in through the drain by action of the air filter blower. This adds complexity to the installation and imposes a maintenance burden.
Any solids will tend to settle out in the tank, requiring periodic maintenance to clean out the accumulated solids.
This is particularly so when the tank is only periodically opened to a drain as this would allow more time for the chips to settle out and not be drained such that a periodic cleaning is necessitated.
This same difficulty is found if an overflow weir were used to receive oil drained from a collection tank.
Another difficulty with the decentralized approach is the cost of individual mist collectors at each station particularly due to the ducting and transitions required.
It is an object of the present invention to provide an oil collection system for a plurality of machine installations which does not involve moving the mist through ducts over a substantial distance but does not require complete oil mist collectors and air filters at each station, and which does not require disposal of oil or chips collected by the oil collector or clean out from a collecting tank.
It is another object of the invention to provide an individual oil mist collector which allows drainage of oil without return air flowing over the collected oil as to recreate a mist or pollution of the air with oil vapor while preventing settling out of chips.